docs: def clear(self, *objs):
          """
          Clear the third relationship table, but not the ModelA or ModelB
          """
          if objs:
              keys = get_objs_columns(objs)
              self.do_(self.model.table.delete(self.condition & self.model.table.c[self.model._primary_field].in_(keys)))
          else:
              self.do_(self.model.table.delete(self.condition))